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Bruno Putzeys Kii Speakers' technology
Bruno Putzeys Kii Speakers' technology
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Old 13th November 2016, 04:12 PM   #1
plasnu is offline plasnu  United States
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Default Bruno Putzeys Kii Speakers' technology

I heard Bruno Putzeys' Kii speakers at the recent NYC audio show, and it seems many people there were quite impressed with them. I felt Kii would sound better than the most mainstream near / midfield studio monitors these days.

They are hypex multiple amp driven active speakers with a new technology, Active Focus Filter, which is probably the same concept as Geithain's cardioid bass.

acoustics

Anyone can explain the detail of this technology? I guess it is probably based on some kind of phase-shifted digital delay line involved, and it can be added to any existing speaker system.

Last edited by plasnu; 13th November 2016 at 04:16 PM.
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Old 13th November 2016, 05:36 PM   #2
LineArray is offline LineArray  Germany
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Hi Plasnu,

Kii "Three" works AFAIK as a monopole below approx. 60Hz and as a cardioid from (middle) bass to midrange.

The two side mounted bass drivers change their roles in midrange and are then used for also increasing the directivity of the midrange unit (at least in lower midrange AFAIK).

That "role changing" of the side mounted bass drivers (being "cardioid front drivers" in bass and "rear drivers" in midrange ...) has been supposed by myself in a german forum - where the speaker was presented - and Bruno confirmed that "trick" in a later post.

So there are some differences to the Geithain concept of cardioids, which maintain the cardioid pattern until the "lower end".

Kii "Three" avoids that also for reasons of efficiency and saving "displacement volume" at LF, which is not unlimited with such a rather small speaker to achieve appropriate levels of sound pressure in lower bass.

Also Bruno Putzeys sees no advantage in maintaining the cardioid pattern to the "lower end".

(Which is where our opinions differ, but nevertheless for such a compact speaker - operating fullrange and not necessarily dependent from a subwoofer - he surely made a good decision ...)
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Last edited by LineArray; 13th November 2016 at 05:52 PM.
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Old 13th November 2016, 09:21 PM   #3
plasnu is offline plasnu  United States
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Line array, thank you very much for the detailed explanation. A lot of the things are still mystery to me, but it's good to know Kii is different from Geithain.

So 2 woofers on the back side work as sub woofers below 60hz?
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Old 13th November 2016, 11:00 PM   #4
LineArray is offline LineArray  Germany
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Hi Plasnu,


No. The 4 woofers work in phase at the low end.

In mid and upper bass the 2 side woofers and the 2 rear woofers make up a cardioid.

Common technique is to give a delay to the rear woofers and apply a lowpass filter to cancel the radiation to the rear.

That is commonly used in PA cardioid subwoofers e.g.

Geithein uses a "resistance box" where the rear sound source used for cancellation is made up by a (passive) flow resistor. The delay and low pass filter effect needed in a cardioid is here provided "acustically" by the cabinet's volume (providing mechanical compliance) and the flow resistor.

The principle is first described by Kalusche 1950. Works well and has been also refined over the decades ...

Kii uses active controlled (filtered) woofers, like common in PA nowadays.
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Last edited by LineArray; 13th November 2016 at 11:13 PM.
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Old 13th November 2016, 11:26 PM   #5
Charles Darwin is offline Charles Darwin  United Kingdom
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In engineering terms Kii is the brute force solution, Geithain the elegant solution to the same problem.
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Old 13th November 2016, 11:39 PM   #6
LineArray is offline LineArray  Germany
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Which is a valuation ...


From a technical - result oriented - point of view, both approaches work.


It is a bit diffcult to morph a cardiod to a monopole at lower bass.

But i know a company also (not geithain) who does even this by using an acoustical/mechanical device:

Technologie - Barth Acoustic Systems


But i "know what you mean" and i am constructing an refining "classical" cardioids myself:

I can see no drawbacks, in the contrary. But engineering effort may be even higher in the classical approach, as you have to care for details you can neglect when solving the problem using multiple drivers and digital/active filters.
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Last edited by LineArray; 13th November 2016 at 11:48 PM.
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Old 14th November 2016, 09:49 AM   #7
Juhazi is offline Juhazi  Finland
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Barth is monopele in bass, at least this line array http://www.barth-acoustic.com/?dl_na....C8HP.Rev2.pdf

But look at these instead! http://kimmosaunisto.net/CardSub/CARDSUB.html
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Old 14th November 2016, 10:05 AM   #8
LineArray is offline LineArray  Germany
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Quote:
Originally Posted by Juhazi View Post
Barth is monopele in bass, at least this line array http://www.barth-acoustic.com/?dl_na....C8HP.Rev2.pdf
...
Hi Juhazi,

that is why i mentioned it with respect to Kii "Three", which is a monopole at the low end too.
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Old 14th November 2016, 10:06 AM   #9
LineArray is offline LineArray  Germany
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Quote:
Originally Posted by LineArray View Post

It is a bit diffcult to morph a cardiod to a monopole at lower bass.
Maybe replace "morph" by "make a transition from".
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Old 16th November 2016, 04:22 PM   #10
plasnu is offline plasnu  United States
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It's interesting to know everyone has different opinions for the LF directivity, Linkwitz prefers dipole, Bruno chooses monopole, Geithain is successful with cardioid, and all seem to be working well...
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